Removable pressure sensitive adhesives (PSA) adhered to a backing, which predictably adhere, yet remain repeatedly peelable from a variety of substrates over a long period of time without damaging or marring the substrate, have many commercial uses. For example, masking tapes, removable labels or office notes, protective films and medical tapes all must quickly adhere to metal, paper, plastics and skin, respectively, but must also peel smoothly away from these varied substrates without leaving behind any adhesive residue on or damaging the surface of a particular substrate.
Ideally, depending on the substrate, the removable adhesive must provide sufficient tack to quickly fix the adhesive to the desired substrate, adequate peel strength to prevent damage of the surface when the adhesive is removed, and have the appropriate cohesive strength to control the transfer of adhesive to the substrate. Cohesive strength must also be controlled so to limit the cold flow of the adhesive on a surface, a process which leads to an undesirable building of peel strength over time.
Typically, the cohesive strength of a PSA may be improved in a variety of ways. For example, cohesive strength may be enhanced through the covalent crosslinking of the adhesive. Some types of chemical crosslinkers are thermally activated and thus cannot be used with hot melt processable PSAs. To covalently crosslink hot melt coated PSAs, one typically must use a post-coating radiation crosslinking process such as one initiated by ultraviolet or electron beam radiation. Such processes require expensive equipment.
It would be beneficial in a hot melt or extrusion process to provide an adhesive that has adequate cohesive strength in the absence of a post-coating crosslinking process.